1. Field of the Invention
The present invention relates to a compound which is useful for acid generation in a resist composition, a resist composition containing the compound, and a method for forming a resist pattern using the resist composition.
2. Description of the Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure with radial rays such as light or electron beams through a mask having a predetermined pattern formed thereon, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.
In general, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Specifically, ultraviolet rays typified by g-line and i-line have hitherto been used. But, nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. In addition, investigations are also being conducted on lithography techniques using an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beams, EUV (extreme ultraviolet radiation), and X rays.
Resist materials are required to have lithography properties such as sensitivity to these exposure light sources and resolution capable of reproducing patterns of minute dimensions.
As a resist material that satisfies these requirements, a chemically amplified resist composition containing a base material component whose solubility in a developing solution changes by the action of an acid and an acid generator component which generates an acid upon exposure, has hitherto been used. For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a positive-type chemically amplified resist composition containing a resin component (base resin) whose solubility in an alkali developing solution changes by the action of an acid and an acid generator component is generally used. If a resist film formed using such a resist composition is selectively exposed at the time of forming a resist pattern, in exposed areas, an acid is generated from the acid generator component, and the polarity of the base resin increases by the action of the generated acid, thereby making the exposed areas soluble in the alkali developing solution. Accordingly, a positive-type pattern in which unexposed areas remain as a pattern is formed upon alkali development. On the other hand, in the case of applying a solvent developing process using a developing solution containing an organic solvent (organic developing solution), when the polarity of the base resin increases, the solubility in the organic developing solution is relatively decreased. Therefore, unexposed areas of the resist film are dissolved in and removed by the organic developing solution, whereby a negative-type resist pattern in which exposed areas remain as a pattern is formed. In this way, the solvent developing process for forming a negative-type resist pattern is sometimes called a negative-type developing process (see, for example, JP-A-2009-025723).
Currently, for example, resins having a structural unit derived from a (meth)acrylic ester in a main chain thereof (acrylic resins) are generally used as a base resin for resist compositions to be used for ArF excimer laser lithography in view of the fact that they are excellent in transparency in the vicinity of 193 nm (see, for example, JP-A-2003-241385).
In addition, as acid generators which are used in a chemically amplified resist composition, various types have been proposed up to date. For example, onium salt-based acid generators, oxime sulfonate-based acid generators, diazomethane-based acid generators, nitrobenzylsulfonate-based acid generators, iminosulfonate-based acid generators, and disulfone-based acid generators are known. In recent years, base resins containing a constituent unit having an acid generator function are also used (see, for example, JP-A-2006-045311).